Glycosides are a main chemical constituent of the mustard family. In short, glycosides are basically carbohydrate glycones (which is a sugar part) bonded to an another part called an aglycone. The bond between them breaks by an enzyme and hydrolysis (hydro-, water; -lysis, breaks) which frees the aglycone group to be used by the body. Many biochemists use the aglycone group to categorizes glycosides; it is what gives them their special actions.

Glycosides are a well-known herbal chemical constituent group. The powerful steroidal cardiac glycosides get a lot of press, after an English herbalist discovered the use of foxglove (Digitalis spp.) for right heart failure in 1785 (Mills, 310). Then there are the well-known poisonous cyanogenic glycosides amygdalin of the Rosacea family and others, mostly in the stone fruits like bitter almond. Prunasin is a glycoside found in another Rosecea member, wild cherry (Prunus serotina), that “…exhibit expectorant, sedative and digestive properties” (Hoffmann, 49). Alcohol glycosides are a part of willow and other salycilic acid-containing plants. The glycosides called anthraquinones are laxatives, as found in senna , aloe and rhubarb (48).

In the mustard family, the glycosides are called glucosilinates and are very pungent. Mostly in the stem and seeds (315).When the plant is damaged, it produces a acrid vapor from the volatile isothiocyanates.

Glucosinolates, also called isothiocyanates, are the glycosides present in the mustard family. Most people don’t need a scientist to tell them that sulfur is a key element of glucosilinates. The pungent onion and garlic of Liliacea also contain sulfur. The glucosinolates are found mostly in the stem and seed and are released when the plant tissue is damaged. Botanically, they act to protect them against predators. Anyone who gardens knows there is an exception to the brassicas best efforts: the white cabbage butterfly and caterpillar. Old farmers know that livestock that eat too much brassicas can develop thyroid, liver and kidney problems. They are, after all, goitergenic; they depress thyroid function. This action can be used to advantage in cases of hyperthyroidism (Hoffmann, 50).

And as anyone who has eating a bit too much wasabi (Wasabia japonica) on their California roll knows that when taken internally, the mustard family is helpful for decongesting the sinuses (50). Externally, mustard oils act as rubefacients that encourage local increase of blood flow. The blisters that can sometimes happen when a mustard poultice is applied too long are the obvious result of this action. Mustard poultices work quite well to break up congestion and pain in the lungs, see here for directions. I have always heard not to use hot water to make to poultice, but until now I never knew why; combining with water above 113 F or 45 C can produce poisonous nitriles. Interestingly, Mills comments that low levels of the same nitriles are produced when boiling cabbage, but nobody seems to be concerned about it (316).

Do we need any more reason to eat our broccoli? Various studies have shown that diets high in brassicas decrease the risk of cancer. This site give a a good overview of some of the different findings, and lots of references. For those of you who wonder how this actually occurs, David Hoffmann explains glucosinolates ‘ role as such:

“Experimental tumor production is greatly inhibited by pretreatment with isothiocyanates. The isothiocyanates interfere with the metabolism of carcinogens by enhancing the activity of several cytochrome P450 enzymes involved in the detoxification processes. They inhibit pro-carcinogen activation…” (50).